The present invention concerns a device for spreading of a top wrapping film during wrapping in a wrapping machine. This wrapping machine is provided with a film distribution sledge, and a film roll being fitted on the sledge, from which wrapping film is arranged to be wound around a product to be packaged in the wrapping machine, this product having been brought into a wrapping station by means of a conveyor or equivalent. The product is wrapped by rotating the film distribution sledge around a vertical central axis of the wrapping station.
More specifically, a top film device is provided which comprises a top-film roll as well as devices for feeding and pulling the top film. These devices are arranged to spread the top film above the product to be packaged and to cut the top film to the specified dimensions. A press plate or equivalent as well is provided, which presses the product to be packaged from above, for the purpose of keeping the product to be packaged in position during the wrapping.
The present invention also concerns a method for the spreading of the top film in wrapping in a wrapping machine, by means of which the wrapping film is wound in the wrapping machine around the product to be packaged which has been brought into a wrapping station by means of a conveyor or equivalent. This film is unwound from a film roll fitted on a film distribution sledge, so that the film distribution sledge is rotated around a vertical central axis of the wrapping station. By means of a top film device provided in this wrapping machine, a top film is spread out above the product to be packaged and the top film is cut off to the specified dimensions. Furthermore, in the wrapping machine, the product to be packaged is kept in position during wrapping by means of a press plate or equivalent that presses the product from above.
In the prior art, a method is known for wrapping of products to be packaged by means of a wrapping film, in which the products to be packaged are brought into the wrapping machine by means of a conveyor which brings the product to be packaged, e.g., on a pallet into the wrapping machine and stops the product in the wrapping machine for the time of the wrapping. During the wrapping, the product to be packaged is kept immobile in the wrapping machine, and the wrapping film is wound around the product so that the roll of wrapping film is rotated around the product.
For the purpose of rotating the roll of wrapping film around the product, the roll is mounted on a film distribution sledge which is provided with suitable members so as to make the tension of the wrapping film appropriate during the wrapping. For the purpose of rotating the film distribution sledge around the product to be packaged, the wrapping machine may be provided with a wrapping crank which is arranged to be rotatable around a vertical central axis of the wrapping station. On the other hand, in such a machine the film distribution sledge is mounted on the wrapping crank to be vertically displaceable.
A second possibility for rotating the film distribution sledge around the product to be packaged, is such that the wrapping machine may be provided with a wrapping circle, circulating around the wrapping station, and on which the film distribution sledge is displaceably mounted. Thus, in such a machine, the film distribution sledge circulates around the product to be packaged in a circle. On the other hand, the wrapping circle is normally mounted on a frame of the wrapping machine to be vertically adjustable.
A significant problem in the prior art wrapping machines and methods, is the fitting of the top film or top sheet onto a product to be packaged, and the need of making the package sufficiently well-sealed. For the spreading of the top film, the wrapping machine is normally provided with a top film roll which is fitted on a stand placed on an upper part of the frame of the wrapping machine. From this stand, the top film is unwound by means of a top film pulling sledge, by means of which the film is pulled across the product to be packaged and thereupon cut off by means of a cutter to the desired length.
Especially in wrapping machines provided with a wrapping crank, the pulling of the top film has been questionable, because it has been necessary to stop the wrapping completely for the time of the pulling of the top film, since it has been necessary to fetch or grasp the top wrapping film by means of the pulling sledge from outside of the circumference of rotation of the wrapping crank. In such conventional wrapping machines, after the top film has been spread out above the product to be packaged and cut off to the desired dimension, the top film pulling sledge returns to its starting position, after which the wrapping has been continued so that the wrapping film to be wound around the product to be packaged binds the top film in its position. Thus, for example, in the case of pallet packages, the spreading of the top film has involved quite a considerable period of time during which the wrapping has been completely interrupted. The length of this time is normally in the order of 15 to 20 seconds.
It has been a further drawback related to the prior art methods and wrapping machines, even though of relatively minor importance, that, since the top film roll is placed outside the circle of rotation of the wrapping crank, the length of the top film unwound has always been considerably longer than would have been necessary in view of the package. Thus, in the prior art methods and machines, the consumption of the top film material has been considerably high.